High-frequency power dissipating termination



A ril 20, 1954 T. N. ANDERSON HIGH-FREQUENCY POWER DISSIPATINGTERMINATION Filed May 7, 1953 INVENTOR. Tare IVY finder-son PatentedApr. 20, 1954 HIGH-FREQUENCY POWER DISSIPAIT ING TERMINATION Tore N.Anderson,

to Airtron, Inc., New Jersey Mountainside, N. Ia, assignor Linden, N.J., a corporation of Application May 7, 1953, Serial No; 353,623 12Claims. (01. 333-22) This invention relates to high frequency powerdissipating terminations "wherein electrical energy is converted intothermal energy for dissipation, and, more particularly, relates toprovisions in such terminations for causing the dissipation ofelectrical energy to be substantially uniformly efifected along alongitudinal dimension of the device.

Such terminations haveheretoior'e been provided both for coaxial cablesand for wave guides to permit testing of power and'other factors inelectronic systems. In such devices, it is common to employ, Within aclosed-end cable or wave-guide termination section, a lining of suitabledissipative material,- usually a ceramic material, to absorb and convertthe electrical energy therein into thermal energy; the resultantheatbeing carried off through the walls of the termination section. Suchlinings have commonly been applied to the entire interior of thetermination section and radiation fins, also, have been providedthroughout the entire length of the exterior of such a terminationsection to facilitate the dissipation of the heat.

Terminations-of the character just described have not been entirely"satisfactory for several reasons. Apparently because or the abrup-th'esswith which the electrical 'energy is received inthe termination by thelatters dissipative material at a sharp transverse line where thedissipative material adjoins aconnected metal condoctor, the conversionto heat becomes consid erably accentuated in the region of the saidjunction, causing relatively quick structural breakdown of thedissipative materialand failure of the device at that location. Withsuch prior structures, also, it has been diflicult to minimizereflection of energy back into the conductcr, thereby giving rise to anobjectionably high standing wave ratio with decreased power in therelated electronic system and test results which are not adequatelydependable. Thementioned disadvantages become more pronounced with themuch higher power now being employed in such electronic systems. I

Accordingly, an important object of this invention is the provision of anovel and improved dissipating termination capable of efli'cientlyconverting electrical energy to=another form of energy for dissipation.

Another important object is the provision, in such a termination, ofimproved means for ef fecting such conversion of-energ'y quite uniformlythroughout the terminations length- Another important object is theprovision of such a .termmati'oniwherein theelectr-ical energy 2 isconverted to thermal energy quiteuniformly along the-length of thetermination, thereby minimizing the total heat developed and avoidinghot spots whichmight cause quick breakdown of the dissipative material.

Another important object is the provision of such a termination whichmay operate at increased peak power and which is capable ofsubstantially completely dissipating whatever elec-- trical energy isflowing through the system without material development of reflectionsor stand ing waves.

Although the present invention may be useful ln-other forms ofconductors, it is particularly useful in wave guides which have greaterpulse power capacity than cables and are more suitable than cables forconducting the shorter wave lengths in the microwave region. The presenttrend to higher power in such shorter wave lengths serves to point upthe importance of the stated objectives in relation to wave guides and,therefore, the present disclosure of this invention is made with respectto Wave guides without, however, limiting the invention exceptasspecifled inth-e claims hereinafter set forth.

As applied to "wave guides, the stated objects are accomplished by atermination which has smooth, uninterrupted, internal surfaces formingdirect continuations of internal surfaces of a wave guide connectedthereto, said surfaces, in the vicinity of the input end ofthetermination, beinginter-tapering surfaces of bodies of conductivemetal and of dissipative material, the metalsurfaces at opposite sidesof the device ascontinuations or" the. interior, conductive surfaces ofthe related wave guide and tapering away, in theform of a wedge, tonon-existence in the direction of the closed or terminal end of thetermination. In the same input vicinity, the dissipative. material isshaped complementally to said wedge to complete the internal walls inwhich thewed'ges are located. The metal wedge maintains a diminishingconductivity of the device in the same longitudinal area thereofwhereembodiment of this invention substantially on the line l--l of Fig.2, i. e., at a plane extending through the broader opposite sidesthereof;

Fig. 2 is a central, longitudinal, sectional view on the line 2-2 ofFig. l, i. e., at a plane extending through the narrower opposite sidesthereof;

Fig. 3 is an end elevational view of the termination as seen from theright end of Figs. 1 and 2;

Fig. 4 is an end elevational view of the termination as seen from theleft end of Figs. 1 and 2; and

Figs. 5 and 6 are transverse, sectional views, respectively, on thelines 5-5 and 6-6 of Fig. 2.

The illustrated termination consists fundamentally of three parts; atubular casing it which may be cast of suitable metal such as analuminum alloy, an inlay l2 of dissipative material, and an end or coverplate 14 held upon the terminal end of the casing by screws 56.

At its input end, its right end as viewed in Figs. 1 and 2, the deviceis provided with a preferably integral connection flange if} havingscrew holes to receive screws (not shown) by which the device may beconnected to a rectangular wave guide or other conducting component inrelated electronic apparatus. Either by special connection or by asuitable switching arrangement, the termination device may besubstituted, for test purposes, for a power output assembly, as, forexample, an antenna circuit.

The termination is formed with what might be termed aconduction-dissipation passage 22 extending from the input end, almostto the opposite or terminal end of the device. This passage, in theillustrated structure, is rectangular in shape in cross-sectionsubstantially throughout its length, preferably being of the same sizeand shape, at the input end, as the interior of the wave guide or othercomponent to which it is connected. The broader diameter of this passageis preferably of uniform dimension throughout the length of the passage,as may best be understood from Fig. 2, while the narrower diameter ofthe passage is preferably of uniform dimension only to an intermediatelocation in the device and, as shown in Fig. l, tapers from thatintermediate location to substantial nonexistence at a location near theter minal end of the device.

The passage 22 has flat surfaces of metal on all four sides thereof inthe vicinity of the input end to the longitudinal extent indicated bydoubleheaded arrows a:-:c in Figs. 1 and 2, the metal thereof being themetal of which the casing 10 is cast. The mentioned flat surfaces ofmetal on the opposite broader sides of said passage are coplanarlycontinued in the form of internal metal wedges 24, which preferably, areintegrally cast as a part of the casing l0. These wedges mayadvantageously be of the approximate longitudinal extent indicated bydouble-headed arrows y-y in Figs. 1 and 2 and are like internal landsdefining therearound the areas occupied by the inlay I2.

The inlay area is in the nature of an elongate, internal, rectangularrecess 26 which has broader and narrower diameters which are greater,respectively, than corresponding broader and narrower diameters of thepassage 22 at the input end of the device. Thus, the dissipative inlay[2 which fills the recess 26 is substantially rectangular in shape, withgradually thickened broad wall portions 28 toward its terminal end andhaving its broad walls acutely bifurcated by the wedges 24 toward theinput end of the termination to form acute angular wings til, 30 whichtaper off to non-existence at points near the input end of narrow walls32 of the inlay which may be of uniform thickness throughout theirlength. In the illustrated embodiment, the broader internal surfaces ofthe inlay and of the wedges defining the passage 22 are coplanarthroughout approximately the input half of the device and the saidbroader surfaces, which are entirely inlay surfaces throughoutapproximately the terminal half of the device, are continuations of saidcoplanar surface portions and converge toward the terminal end asindicated at 34 in Fig. 1. The inner surfaces of the wedges 24,preferably, are broached during manufacture to render them smooth,thereby offsetting in the corresponding end of the device, someundesirable effects arising from the relative roughness of the surfacesof the inlay l2, particularly at the wings 3&3.

The casing II] is suitably fitted or formed with a plurality of integralperipheral fins 3% to facilitate the transfer of heat from said casingto the surrounding air. These fins may be provided, as shown in Figs. 1and 2, only toward the input end of the device. If they extend from apoint toward the right of the input end of the inlay IE to a point wellbeyond the wedges, as shown in the drawing, the fins function adequatelyadjacent to the area where greatest heat generation occurs; and theremaining portion of the casing suffices without such peripheral fins totransfer, to ambient atmosphere, the heat developed toward the terminalend of the device.

The dissipative inlay 52 may be of any suitable material for absorbingelectrical energy and converting it to thermal energy and should becapable of withstanding the high temperature developed by the absorptionof the high power in a related wave guide. It may advantageously be acomposition formed by intermixing and ball-milling two parts, by weight,of flaked graphite and three parts of lumnite cement and by thenadmixing water only in a quantity sufficient to form a plastic cementwhich is workable as hereinafter indicated.

In making the device, the casing it is first cast to its desired shape,after which the surfaces of the wedges 2d are broached smooth. A core ormandrel corresponding in shape to the desired shape of the passage 22and coated with suitable anti-adhesion material, is extended into theinput end of the casing and suitably held fixedly therein. Then, withthe casing held in vibrating device in an upright position with itsterminal end uppermost, the previously prepared dissipative material ispoured very slowly into the then-open terminal end of the device andpermitted to gravitate into the inlay space until the latter is filled;the vibration of the device, meanwhile, functioning to free any airbubbles from the dissipative mix. After the mix has set, the settingtime usually being an hour or more, the mandrel is removed and thedevice is subjected to a week, more or less, of curing in air and thensuitably baked. The baking, where the inlay mix is of the generalcharacter suggested herein, may advantageously be at approximately 275F. for about twenty-four hours and then at about 700 F. for about eighthours; the oven being permitted to cool to about 200" F. before thetermination is removed therefrom.

After completion of the baking step, the de vice is filled with animpregnating solution of about silicone resin and 10% toluol (by vol-5.. time) and subjected to a vacuum while thus filled until bubblingfrom the dissipative inlay substantially ceases, after which the excessof this solution is drained oil and wiped from all exposed metal innerand outer surfaces. Thereafger, the device is again baked, first atabout 27 at about 500 F. for about eight hours. The inlay, thus, isfixedly impregnated and coated to minimize moisture absorption in thepresence of humidity.

In operation, the electrical energy entering the device, at its inputend, in the form of waves, apparently moves between the wedges 24 withthe peak of the waves following the center line of the wedges while thewaves opposite fringes undergo gradually increasing absorption from thegradually enlarging areas of the wings 30 of dissipative material. Thisfringe absorption causes absorption, also, at the wave peaks so thatupon reaching the ends of the wedges the electrical energy has beenconverted, to such an extent, to thermal energy that, in the remainderof the device, the dissipative material alone suflices to complete theabsorption of the electrical energy and the resultant heat in saidremainder of the device may be carried oif adeuately through thenon-finned portion of the casing It. Thus, the heat generated is notunduly localized at any one point and the total heat generated isminimized, leading to long life for the inlay l2.

It has been found, also, that terminations according to this inventionmay operate at increased peak powers, apparently because of theavoidance of hot spots, and that reflection of energy is minimized witha resulting minimum in standing wave ratio. In addition, it appears thatas there is no development of excessive heat at any point in the inlay,steaming of the inlay is minimized, thereby substantially obviating the.passage of steam vapor into a related wave guide and the undesirablecondensation of such vapor which could adversely affect the wave guidestransmission characteristics.

Without attempting to recite herein all the pessible variations of thisinvention, it may be noted that the wedges 24 may be of various relativedimensions; that the broad concept of using such wedges as hereindescribed may also be varied by disposing the wedges in the narrowerwalls rather than in the broader walls of a rectangular termination foruse with a rectangular wave guide; and that such wedges may be used, inthe manner and for the purposes stated, in circular wave-guideterminations. In circular wave-guide terminations, the bases of themetal wedges should preferably be spaced from each other much as thebases of the wedges 24 in the accompanying drawing are spaced from eachother by the dissipative material in the narrower walls of thetermination.

As the present inventive concept obviously could be utilized in meansother than disclosed herein, the scope of this improvement should not belimited except as set forth in the following claims.

What I claim is:

l. A power dissipating termination comprising a tubular body ofdissipative material, closed at a terminal end thereof and of across-sectional, inside size and shape toward the opposite, input end ofsaid body, substantially similar to a recess opening in a conductingelement to which the termination is adapted for connection, and

F. for about twenty-two hours and then 6: a wedge of conductive theinput end of a wall of said body and having its interior surfacedirectly continuous with adjacent surfaces of the dissipative body.

2. A power dissipating termination comprising an elongate, hollow bodyof dissipative material, closed at a terminal end thereof and interiorlyof rectangular shape in cross-section, and a pair of conductivewedge-shaped members fixedly associated with and extending-into saiddissipative body toward the latters opposite, input end with wedge.points thereof directed toward the terminal end of the said body andwith opposed inner faces of the wedge-shaped members coplanar withcorresponding inner faces of adjacent portions of said dissipative body.

3. A power dissipating termination comprising a casing of conductivemetal and a lining therein of dissipative material defining therewithinan electrical energy-dissipating passage of rectangular shape intransverse section, and wedgeshaped, conductive, metallic portionsintegral with said casing at opposite sides thereof toward an input endof the casing and directed toward the opposite end of the casing andextending into the dissipative material at corresponding opposite sidesof said passage, thereby forming dissipative wings at opposite sides ofsaid wedgeshaped portions; the latter having substantially fiat insidesurface which are substantially coplanar and continuous with respect toadjacent inside surfaces of dissipative lining material at saidcorresponding opposite sides of said passage.

4. A power dissipating termination according to claim 3, furthercharacterized in that the said passage is non-equilaterally rectangularin transverse sectional shape and the said wedge-shaped portions are inpartially embedded relationship with respect to the dissipative liningmaterial at the broader sides of said passage.

5. A power dissipating termination according to claim 3, furthercharacterized in including plural radiation fins at the exterior of thecasing in a longitudinal region of the latter correspondingsubstantially to the longitudinal region wherein the said wedge-shapedportions are located.

6. A power dissipating termination according to claim 3, furthercharacterized in that the said inside surfaces of the wedge-shapedconductive portions are substantially smooth.

'7. A power dissipating termination according to claim 3, furthercharacterized in that said lining includes moisture-resistant materialon its exposed surfaces.

8. A power dissipating termination according to claim 3, furthercharacterized in that the said passage extends toward the terminal endof the device substantially beyond the said wedgeshaped portions and inthat the lining walls defining the sides of the said extended portion ofthe passage which are continuations of the sides having the wedge-shapedportions therein converge and come together to close the terminal end ofsaid passage.

9. A power dissipating termination according to claim 8, furthercharacterized in that the said converging lining walls increase inthickness toward their terminal ends substantially in proportion to theconvergence of said converging walls.

10. A power dissipating termination comprising a tubular body ofdissipative material, closed at a terminal end thereof and of across-sectional, inside size and shape toward the opposite, input end ofsaid body, substantially similar to a recess material extending i topening in a conducting element to which the termination is adapted forconnection, and a pair of opposed wedges of conductive materialextending into the input end of said body at opposite sides thereof withtheir converging sides directed generally toward the terminationsterminal end and having their interior surfaces directly continuous withadjacent surfaces of the dissipative body.

11. A power dissipating termination according 10 to claim 10, furthercharacterized in that said wedges are spaced from each other.

12. A power dissipating termination according to claim 10, furthercharacterized in that the said wedges extend only into an input-endportion of the termination which, with said wedges therein, is ofuniform diameter throughout its length.

No references cited.

